Police investigators walk past a condo building in Longueuil, Montreal, Quebec, Canada, on September 21, 2020. (Photo by Reuters)

Canadian police say a letter, containing a deadly poison, has apparently been sent to the White House from Canada, as police searched an apartment in a Montreal suburb in connection to the arrest of a woman in the US over the ricin-filled envelope.

US authorities arrested a woman at the US-Canada border near Buffalo, New York on Sunday on suspicion she sent the deadly poison by mail, addressed to the White House.

The arrest came after they intercepted a ricin-filled envelope before it reaches to the White House on Saturday.

The suspect, whose name was not released, has joint Canadian and French citizenship.

We can�t confirm that she lived in (the apartment), but it is connected to her, said the Royal Canadian Mounted Police (RCMP).

The woman will appear on Tuesday in a court in Buffalo, according to a spokeswoman for the federal court in the Western District of New York.

Our Chemical, Biological, Radiological, Nuclear, Explosives team (CBRNE) is leading the operation, the RCMP said.

It said that a total of six letters were sent, one to the White House and five to Texas.

On Saturday, Canadian police confirmed the White House letter had apparently been sent from Canada and said the FBI had requested assistance.

The envelope was intercepted at a government mail center before it arrived at the White House.

RCMP officer Charles Poirier said, We believe a total of six letters were sent, one to the White House and five to Texas.

Poirier did not say where in Texas the envelopes were mailed, but the police department in Mission, Texas, received a suspicious letter within the last week.

The department did not open the envelope and turned it over to the FBI, Art Flores, a spokesman for the department, said.

Flores also said that police had arrested the woman now believed to be held in Buffalo in early 2019, but said he did not have records related to the arrest and referred further inquiries to the FBI.

The FBI has launched an investigating into suspected ricin letters sent to law enforcement and detention facilities in South Texas.

Citing a law enforcement source, Reuters said the FBI has not found any link to political or terrorist groups so far.

There have been several prior instances in which US authorities have been targeted with ricin sent through the mail.

Back in 2018, a Navy veteran was arrested and confessed to sending envelopes to President Donald Trump and members of his administration that contained the substance from which ricin is derived.